Remove Double trailing slash - open cart - .htaccess

Question

i have been contiously upgrading my htaccess file. however, there are 2 issues I just cant seem to fix. I have tried several approaches but nothing really worked for me.
my website: https://www.zeroohm.com/
my questions:
How can I remove the extra trailing slash when i go to zeroohm.com
currently, if i go to zeroohm.com, it redirects to https://www.zeroohm.com//
if i go to www.zeroohm.com/robots.txt/ , it stops me from viewing my robots.txt file (an error occured while processing this directive). how can i fix this? this problem happens to sitemap.xml and it is causing problems with webmaster tool too.
C. any ideas on improving my re-directs?
my htaccess file
RewriteEngine On
RewriteCond %{HTTP_HOST} ^zeroohm\.ae$ [OR]
RewriteCond %{HTTP_HOST} ^www\.zeroohm\.ae$
RewriteRule ^/?$ "http\:\/\/www\.zeroohm\.com\/\$1\/" [R=301,L]
# check if url has www or not, add www if not available. if avaiable dont do anything.
RewriteCond %{HTTP_HOST} !^$
RewriteCond %{HTTP_HOST} !^www\. [NC]
RewriteRule ^(.*) https://www.%{HTTP_HOST}%{REQUEST_URI}/ [R=301,L]
#end
# force incoming traffic coming from HTTP to Https
RewriteCond %{HTTPS} !on$
RewriteRule ^(.*) https://%{HTTP_HOST}%{REQUEST_URI} [R=301,L]
#end
#force trainling slash
RewriteBase /
RewriteCond %{REQUEST_URI} !(/$|\.)
RewriteCond %{REQUEST_URI} /+[^\.]+$
RewriteRule ^(.+[^/])$ %{REQUEST_URI}/ [R=301,L]
#end of force trailing slash
# 1.To use URL Alias you need to be running apache with mod_rewrite enabled.
# 2. In your opencart directory rename htaccess.txt to .htaccess.
# For any support issues please visit: http://www.opencart.com
# For security reasons, Option followsymlinks cannot be overridden.
#Options +FollowSymlinks
Options +SymLinksIfOwnerMatch
# Prevent Directoy listing
Options -Indexes
# Prevent Direct Access to files
<FilesMatch "\.(tpl|ini|log)">
Order deny,allow
Deny from all
</FilesMatch>
# cache to keep it at client pc
<ifmodule mod_expires.c>
Expiresactive on
# set default
Expiresdefault "access plus 24 hours"
Expiresbytype image/jpg "access plus 1 months"
Expiresbytype image/gif "access plus 1 months"
Expiresbytype image/jpeg "access plus 1 months"
Expiresbytype image/png "access plus 1 months"
Expiresbytype text/css "access plus 1 months"
Expiresbytype text/javascript "access plus 1 months"
Expiresbytype application/javascript "access plus 1 months"
Expiresbytype application/x-shockwave-flash "access plus 1 months"
</ifmodule>
#gzip compression
AddOutputFilterByType DEFLATE text/plain
AddOutputFilterByType DEFLATE text/html
AddOutputFilterByType DEFLATE text/xml
AddOutputFilterByType DEFLATE text/css
AddOutputFilterByType DEFLATE application/xml
AddOutputFilterByType DEFLATE application/xhtml+xml
AddOutputFilterByType DEFLATE application/rss+xml
AddOutputFilterByType DEFLATE application/javascript
AddOutputFilterByType DEFLATE application/x-javascript
# SEO URL Settings
# If your opencart installation does not run on the main web folder make sure you folder it does run in ie. / becomes /shop/
RewriteRule ^sitemap.xml$ index.php?route=feed/google_sitemap [L]
RewriteRule ^googlebase.xml$ index.php?route=feed/google_base [L]
RewriteRule ^download/(.*) /index.php?route=error/not_found [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_URI} !.*\.(ico|gif|jpg|jpeg|png|js|css)
RewriteRule ^([^?]*) index.php?_route_=$1 [L,QSA]
#libwww-perl security fix
RewriteCond %{HTTP_USER_AGENT} libwww-perl.*
RewriteRule .* ? [F,L]
RewriteCond %{THE_REQUEST} \ /index\.php\?_route_=?([^&\ ]*)
RewriteRule ^ /%1? [R=301,L]

Answer 1

You can keep these rules in your site root .htaccess:
RewriteEngine On
RewriteBase /
RewriteCond %{HTTP_HOST} ^(?:www\.)?zeroohm\.ae$ [NC]
RewriteRule ^ http://www.zeroohm.com%{REQUEST_URI} [R=301,L,NE]
# check if url has www or not, add www if not available. if avaiable don't do anything.
RewriteCond %{HTTP_HOST} !^www\. [NC,OR]
RewriteCond %{HTTPS} off
RewriteCond %{HTTP_HOST} ^(?:www\.)?(.+)$ [NC]
RewriteRule ^ https://www.%1%{REQUEST_URI} [R=301,L,NE]
#force trailing slash
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_URI} !(/$|\.)
RewriteCond %{REQUEST_URI} /+[^\.]+$
RewriteRule [^/]$ %{REQUEST_URI}/ [R=301,L]
#libwww-perl security fix
RewriteCond %{HTTP_USER_AGENT} libwww-perl.*
RewriteRule ^ - [F,L]
RewriteCond %{THE_REQUEST} \ /index\.php\?_route_=?([^&\s]*)
RewriteRule ^ /%1? [R=301,L]
RewriteRule ^sitemap\.xml$ index.php?route=feed/google_sitemap [L,QSA,NC]
RewriteRule ^googlebase\.xml$ index.php?route=feed/google_base [L,QSA,NC]
RewriteRule ^download/ /index.php?route=error/not_found [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_URI} !.*\.(ico|gif|jpg|jpeg|png|js|css)
RewriteRule (.*) index.php?_route_=$0 [L,QSA]
Clear your browser cache before testing this change.