Promariner is US based and you will find many of the same products (just under different Badges), but for some reason they do not list the Smart regs and battery to battery chargers.
http://www.pmariner.com/products.php
Ample Technology
http://www.amplepower.com/products/sarv3/index.html
There is some good info on this site too
Chris, as far as I am aware only Sterling produce the battery to battery chargers, you didnt mention 2 different tow vehicles before (not that I noticed anyway)and the devil is in he details.... If you Go the invertor route, probably a sterling 20 to 40 Amp charger is best (for speed of charging) not cheap though My 30 A cost £259 List (mind you I didnt pay anything like list price, went to factory Met Charles Sterling and Paid in cash)