Here is output from debugging of rewriterule when using the following rewrite rule syntax on Plone 5.1 with CentOS 7.4:
RewriteRule ^/(.*) http://localhost:8080/VirtualHostBase/http/%{HTTP_HOST}:80/VirtualHostRoot/$1 [P,L]
And just hitting: http://www.rpgbus.com/rpgbus (but don't want it showing that /rpgbus):


[Sat Jul 07 01:43:40.676219 2018] [rewrite:trace2] [pid 9254] mod_rewrite.c(470): [client 98.247.9.249:58822] 98.247.9.249 - - [go1.dev2dev.com/sid#7fc4670ad9f8][rid#7fc467103c80/initial] init rewrite engine with requested uri /rpgbus
[Sat Jul 07 01:43:40.676289 2018] [rewrite:trace3] [pid 9254] mod_rewrite.c(470): [client 98.247.9.249:58822] 98.247.9.249 - - [go1.dev2dev.com/sid#7fc4670ad9f8][rid#7fc467103c80/initial] applying pattern '^/(.*)' to uri '/rpgbus'
[Sat Jul 07 01:43:40.676308 2018] [rewrite:trace2] [pid 9254] mod_rewrite.c(470): [client 98.247.9.249:58822] 98.247.9.249 - - [go1.dev2dev.com/sid#7fc4670ad9f8][rid#7fc467103c80/initial] rewrite '/rpgbus' -> 'http://localhost:8080/VirtualHostBase/http/www.rpgbus.com:80/VirtualHostRoot/rpgbus'
[Sat Jul 07 01:43:40.676318 2018] [rewrite:trace2] [pid 9254] mod_rewrite.c(470): [client 98.247.9.249:58822] 98.247.9.249 - - [go1.dev2dev.com/sid#7fc4670ad9f8][rid#7fc467103c80/initial] forcing proxy-throughput with http://localhost:8080/VirtualHostBase/http/www.rpgbus.com:80/VirtualHostRoot/rpgbus
[Sat Jul 07 01:43:40.676326 2018] [rewrite:trace1] [pid 9254] mod_rewrite.c(470): [client 98.247.9.249:58822] 98.247.9.249 - - [go1.dev2dev.com/sid#7fc4670ad9f8][rid#7fc467103c80/initial] go-ahead with proxy request proxy:http://localhost:8080/VirtualHostBase/http/www.rpgbus.com:80/VirtualHostRoot/rpgbus [OK]
[Sat Jul 07 01:43:41.921014 2018] [rewrite:trace2] [pid 9254] mod_rewrite.c(470): [client 98.247.9.249:58822] c-98-247-9-249.hsd1.wa.comcast.net - - [go1.dev2dev.com/sid#7fc4670ad9f8][rid#7fc4670ffc60/initial] init rewrite engine with requested uri /rpgbus//++theme++barceloneta/less/roboto/roboto-medium.woff, referer: http://www.rpgbus.com/rpgbus//++theme++barceloneta/less/barceloneta-compiled.css
[Sat Jul 07 01:43:41.921071 2018] [rewrite:trace3] [pid 9254] mod_rewrite.c(470): [client 98.247.9.249:58822] c-98-247-9-249.hsd1.wa.comcast.net - - [go1.dev2dev.com/sid#7fc4670ad9f8][rid#7fc4670ffc60/initial] applying pattern '^/(.*)' to uri '/rpgbus//++theme++barceloneta/less/roboto/roboto-medium.woff', referer: http://www.rpgbus.com/rpgbus//++theme++barceloneta/less/barceloneta-compiled.css
[Sat Jul 07 01:43:41.921087 2018] [rewrite:trace2] [pid 9254] mod_rewrite.c(470): [client 98.247.9.249:58822] c-98-247-9-249.hsd1.wa.comcast.net - - [go1.dev2dev.com/sid#7fc4670ad9f8][rid#7fc4670ffc60/initial] rewrite '/rpgbus//++theme++barceloneta/less/roboto/roboto-medium.woff' -> 'http://localhost:8080/VirtualHostBase/http/www.rpgbus.com:80/VirtualHostRoot/rpgbus//++theme++barceloneta/less/roboto/roboto-medium.woff', referer: http://www.rpgbus.com/rpgbus//++theme++barceloneta/less/barceloneta-compiled.css
[Sat Jul 07 01:43:41.921108 2018] [rewrite:trace2] [pid 9254] mod_rewrite.c(470): [client 98.247.9.249:58822] c-98-247-9-249.hsd1.wa.comcast.net - - [go1.dev2dev.com/sid#7fc4670ad9f8][rid#7fc4670ffc60/initial] forcing proxy-throughput with http://localhost:8080/VirtualHostBase/http/www.rpgbus.com:80/VirtualHostRoot/rpgbus//++theme++barceloneta/less/roboto/roboto-medium.woff, referer: http://www.rpgbus.com/rpgbus//++theme++barceloneta/less/barceloneta-compiled.css
[Sat Jul 07 01:43:41.921119 2018] [rewrite:trace1] [pid 9254] mod_rewrite.c(470): [client 98.247.9.249:58822] c-98-247-9-249.hsd1.wa.comcast.net - - [go1.dev2dev.com/sid#7fc4670ad9f8][rid#7fc4670ffc60/initial] go-ahead with proxy request proxy:http://localhost:8080/VirtualHostBase/http/www.rpgbus.com:80/VirtualHostRoot/rpgbus//++theme++barceloneta/less/roboto/roboto-medium.woff [OK], referer: http://www.rpgbus.com/rpgbus//++theme++barceloneta/less/barceloneta-compiled.css
[Sat Jul 07 01:43:42.052213 2018] [rewrite:trace2] [pid 9252] mod_rewrite.c(470): [client 98.247.9.249:58828] 98.247.9.249 - - [go1.dev2dev.com/sid#7fc4670ad9f8][rid#7fc467101c70/initial] init rewrite engine with requested uri /rpgbus/plonejsi18n, referer: http://www.rpgbus.com/rpgbus
[Sat Jul 07 01:43:42.052269 2018] [rewrite:trace3] [pid 9252] mod_rewrite.c(470): [client 98.247.9.249:58828] 98.247.9.249 - - [go1.dev2dev.com/sid#7fc4670ad9f8][rid#7fc467101c70/initial] applying pattern '^/(.*)' to uri '/rpgbus/plonejsi18n', referer: http://www.rpgbus.com/rpgbus
[Sat Jul 07 01:43:42.052282 2018] [rewrite:trace2] [pid 9252] mod_rewrite.c(470): [client 98.247.9.249:58828] 98.247.9.249 - - [go1.dev2dev.com/sid#7fc4670ad9f8][rid#7fc467101c70/initial] rewrite '/rpgbus/plonejsi18n' -> 'http://localhost:8080/VirtualHostBase/http/www.rpgbus.com:80/VirtualHostRoot/rpgbus/plonejsi18n', referer: http://www.rpgbus.com/rpgbus
[Sat Jul 07 01:43:42.052294 2018] [rewrite:trace2] [pid 9252] mod_rewrite.c(470): [client 98.247.9.249:58828] 98.247.9.249 - - [go1.dev2dev.com/sid#7fc4670ad9f8][rid#7fc467101c70/initial] forcing proxy-throughput with http://localhost:8080/VirtualHostBase/http/www.rpgbus.com:80/VirtualHostRoot/rpgbus/plonejsi18n, referer: http://www.rpgbus.com/rpgbus
[Sat Jul 07 01:43:42.052303 2018] [rewrite:trace1] [pid 9252] mod_rewrite.c(470): [client 98.247.9.249:58828] 98.247.9.249 - - [go1.dev2dev.com/sid#7fc4670ad9f8][rid#7fc467101c70/initial] go-ahead with proxy request proxy:http://localhost:8080/VirtualHostBase/http/www.rpgbus.com:80/VirtualHostRoot/rpgbus/plonejsi18n [OK], referer: http://www.rpgbus.com/rpgbus