NP, merged posts.
I think the biggest favour you can do yourself at this point id learning to mod without SAMI - it's really not hard, and opens the door to alot more freedom and the ability to achieve the sort of results you're looking for. One of our admins Gerard wrote this thread a long time ago but it's still hugely relevant and useful.
http://www.thegtaplace.com/forums/topic/5959-sa-modding-guide/
I'm pretty sure you'll be able to give any car the ability to tow by leaving the handling/cfg files unchanged after you install a mod, instead of replacing the lines. This means your range rover will handle like a towtruck but will keep the towing, but you can change the handling later on once you learn the values that the handling file uses. Which usefully are explained here.
edit: i know it's kinda hard to get your head around at first, but investing the time to learn pays off.