I've still got my beseler 67, which has the reversible baseboard. I build a plywood box, about 8" square x 10" high, and mounted the same thread t-nuts to it as the enlarger base; and the box is t-nutted onto my work table. I can go very big with that setup, or do 8x10's. It's all fastened together with knurled (threaded) knobs, and it's easy to level with shims (I've got a chopped up credit card under one corner).
My challenge after that was what to put under my paper - found a formica tabletop at Ikea, about 26" x 40" with white laminate - 11 bucks.
I've looked at the plastic trays they sell to put under dog training cages - they go up to about 40", but are less than 2" deep - seems potentially messy. But I did get three 24x28 trays from eBay for $80 - they're usually 80-ish each.