This is on my list of things I'd like to try someday - but I'm waiting for the right trailer to come along for that.
I'd do it with a 16'
Scamp, but the basic idea works with any of the eggs where the interior fittings are molded independently then riveted in (
ie not a Burro).
My basic plan would be to remove the cabinets next to the bed out of the trailer (easier said than done given the assorted electrical/gas/water lines and appliances). Then take each of them and slice a 12" segment out of the middle (makes sense to line one side up with existing appliance/door/drawer holes). The two remaining halves would then be spliced together using your basic
fiberglass repair approach. This part will undoubtedly require the relocation or removal of some of the appliances (On the basic 16'
Scamp, I'd swap the icebox for a 110
fridge and move it forward, I'd also eliminate the range and/or the sink). The cabinets then get reinstalled leaving a 12" gap in the back. The gap is then filled with plywood cabinets painted white (to match). These are the same height as the benches and extend them. You could either use the stock table with a 12" extension OR build a new longer table using the original hardware.
Fiddly bits: This also requires moving the iron upper cabinet support on the roadside, which itself probably requires the movement of the under-cabinet
lighting also. Depending on the trailer, it might also require a little filling of old vent/access/etc holes and cutting of new ones. This obviously kills a lot of the storage area in the trailer. It's even worse in a 13-footer. I'd make up for the lost storage by adding more overhead storage over the bed area along the curb and road sides.
Mike