Onan corner the market for RV and that is why is so expensive - no competition. New 4000 cost form 3000 to 4000, while 4000 portable cost 600. 3500 Champion will fit into space, but there is problem with cooling. Will have to add a fan to blow down, but Champion is not reliable. I like the Ryobi - less noisy and less fuel. Honda is the best and 1/3 the price that Onan. Yes, some mods will have to be made, but I believe that will be worth in the long run. Yes, Onan is "plug and play", so a Windows for computers, but I run Linux on mine.