this could be a very creative idea, kinda like taking that pond foam and putting it in the middle, then lining that up with rocks to make it look a little more natural but cleaning the glass could be a pain i think. if i were gonna combine 2 tanks id get one at least 6 feet long like a 125. yes, you were able to have both tanks sump-less because they were relatively smaller tanks. with the larger tanks youd def need a sump. if i were you id try to sell both of the skimmers or trade* for a octopus or something along those lines... i personally like the octopus RECIRC 200 (i think i havent looked at em in a while). good luck!
Akbar