I got a 18” tall fiberglass top off craigslist for $200...deals are out there. Junkyard had them for about the same price here in San Diego.
I’ve thought about a rooftop tent on top of some Thule bars on top of my high top. Extra sleeping area. Seems like it could be an interesting build. You could reinforce the fiberglass with plywood and fiberglass or an aluminum frame and fiberglass the pop-up sleeper to the high top. That would be some custom shit. Rhino line or Raptorline it all white and it might look pretty bomber.
2006 RB E250 Ford High top, Diesel 6.0 Bullet Proofed (ouch $) 4" Camburg Eng. Lift, Method Wheels, 33" Toyo AT, RB50 interior (homebuilt)