RewriteCond %{REQUEST_URI} !^/~error/.*
RewriteCond %{REQUEST_URI} !^/~icons/.*
RewriteCond %{LA-U:REQUEST_FILENAME} !-F
RewriteRule ^(.*[^/])$ $1/ [L,R]

RewriteCond %{REQUEST_URI} !^/~.*
RewriteCond %{REQUEST_URI} !^/error/.*
RewriteCond %{REQUEST_URI} !^/icons/.*
RewriteRule ^/(.+)$ /~$1/ [PT]