.htaccess: hiding subdomain with proxy redirect / rewrite - .htaccess

Question

I need to access my site that sits in a subfolder from my domain.
The challenge - Due to my hosting structure, all sites are on the master domain's server in subfolders. Domains are mapped to those folders for each site. The master domain, however, is mapped to the server root like this -
• /www/ (root of www.masterdomain.com)
/folder 1/ (root of www.site1.com)
/folder 2/ (root of www.site2.com)
/folder 3/ (root of www.site3.com)
/folder 4/ (desired root of master domain)
If i install my CMS in folder 4 everything is fine, BUT the CMS code creates new assets in the server root (using DOCUMENT_ROOT i think), NOT in the subfolder.
Attempted fix 1:
Use a rewrite to remove subfolder and set all paths to include subfolder.
Failed - CMS acts as desired, but assets still created in the root.
Attempted fix 2:
Map a subdomain to the folder and rewrite URL to remove subdomain.
Failed: CMS works on subdomain and creates assets in the subfolder (win!), but can't rewrite a subdomain.
Attempted fix 3:
Map a subdomain to the folder, and use a proxy flag from the main domain to load content from it invisibly.
Progress made! Main homepage displays with the correct URL, however linked files and subfolders do not work.
So i can now reach my web app from:
app.exampledomain.com (app works perfectly on all fronts)
OR
exampledomain.com (proxy in effect, all subfolders and links broken)
Here's my htaccess:
Options +FollowSymLinks
RewriteEngine On
RewriteBase /
# Proxy subfolders
RewriteRule ^exampledomain.com/(.+?)?$ http://app.exampledomain.com/$1 [P,L,NC]
# Proxy main
RewriteRule ^(exampledomain.com)?$ http://app.exampledomain.com/ [P,L,NC]
So why are my subfolders / assets not working? Problem with the .htaccess? Bad logic?
Important notes -
Subfolder pages are called index.php so can be accessed from -
/folder/
The broken links on the page are in this format -
js/foundation.min.js
Thanks.

Answer 1

RewriteRule knows nothing about domain names, it works only with a local path.
Instead, check the domain name in the RewriteCond:
RewriteCond %{HTTP_HOST} ^(www\.)*exampledomain\.com$ [NC]
RewriteRule (.*) http://httpd.apache.org/$1 [P,L]
But using mod_alias or VirtualHost would be a more correct decision here.