If you're as anal about fitting panels to the various bump outs and other irregularities of a van's interior that process can certain tax the gray matter and patience too.
I've purchased all sorts of pattern making tools to do cardboard mock ups before cutting the plywood and FRP panels. Those have a learning curve so that sucks up some time too.
I'm in process of re-installing a rear heater only unit to accommodate other changes to my cargo-only work van. Once one portion is finished something better occurs and then the mental battle begins; change it or move on? I've spent probably 40 actual hours trying to successful fit just two panels in place, almost done---I think?!? Oh well---its more fun doing this than I care to admit otherwise I'd just have left the van completely bare.
That's nice looking cabinet work BTW.