Did you pay retail or cost for those panels?
Anyway, plan to pay about $45k for a 2021 Ecoboost AWD SRW 350 (9.5k GVWR) 156"WB Transit that has all the nice options and will weigh about 4,650 pounds so max payload is 4,850 . This gives you roughly 3.3k pounds for a build if you want a good margin of 1.5k for CCC.
Winnebago with the Ekko definitely needs the DRW with 11k GVWR, which gives you 6,080 max payload or roughly 1.2k more pounds for your build. Especially if you want to stay close to the 1.5k CCC, which is the number Winnebago claims for their smaller 22A model. I've heard through the grapevine that the longer 24C model (25') may only have a CCC of about 1k pounds as that chassis actually has a slightly lower max payload at 6,070 pounds, but obviously the build out will weigh more.