2 4Kw inverters is a bad idea. If the owner turns too many inverter loads on while driving he'll learn what a 50DN alternator cost. Also, realize the cost has to include new 4/0 battery to inverter cables. The marine grade ones are $10/ft!

As coaches get older there is less resale impact on changes, especially those that can be explained. I have eliminated one of two Trace 4Kw inverters replacing it with a transfer switch for one owner. This owner's use of their coach didn't justify inverter replacement. It also afforded him the opportunity to reduce his battery bank size. At $500+ per battery and 120-160 pounds per battery, why invest in dead weight.

Given the age of this coach, modernize the electrical system solely to meet the owner's needs.