If you want to try AL wheels I think these might just fit but you'll need to verify the size - https://www.amazon.com/1976-1992-ALU...Z7JP5JP2P9WYY1
I think, but again you need to verify, you need a 19.5 X 6" wheel with a 10 - 7.25" bolt pattern and a 5.25 center bore. Check the wheel offset also. Ford F53 wheels won't fit on a Workhorse. Bolt pattern is bigger by over an inch. Same for the center bore.
Also, as mentioned, you might need to replace the studs with something longer. Somewhat of an easy job on the daily driver but I'm not so sure it would be a driveway project to attempt on an RV. Probably need a press just to get the old studs out and the new in addition to the level of effort just to get the wheel hubs off the axles. If you do plan to attempt might as well replace the wheel bearings, brake rotors and brake pads while everything is apart.