[starchy]

what i wanna do ultimately is paint these white and and have 'em looking like one contiguous sheet rather than 3 panels. i'll probably just go the easy route and run some strip of ornamental ceiling moulding across where the panels meet one another.

 

[rjcarter3]

I would go with the strips - just rip them from what you have. That's what I did and looks good. Looks like you used the exact same plywood that I did. Keep in mind that your van is going to bend and flex, so even if you get those joints looking good now it might not hold up. You could try, though. Maybe glue them together along the edges, drill some wood braces to keep them even while drying, sand, caulk, and paint.

I will say though that I had to take down my ceiling several times to redo some wiring stuff before I was done-done. Might be more challenging if you have to do that and you've already glued them into one piece.

 

[JohnnyRambles]

If your plan is to paint it white, I'd rip down some narrow strips of white PVC molding and round the two long edges with a router. That way you won't have the rough layered edges to deal with and the softened edges should help to make it look more uniform.

 

[MsNomer]

I used the same ply that you used. No way to hide the seams except with molding. I used 1x4 stripped to 1/8” thick.

When I painted, I did not feather, but took the opposite approach with random strokes. I’m really glad I did

It is holding up well—this is after 7 years.