Some thoughts and comparisons, checking what stores had available, and what finances I was willing to spend on temporary enclosures, Tony came up with an idea. If they've been living together out at the resort, maybe they could live together here as well - but not in a small store-bought cage. They'd need to have more space. Menards sells fence panels, why not make a small enclosure, add a tarp roof, and a quick wooden step up so they can get up off the ground? Total investment for this one 5x5' metal fenced enclosure (with gate door, tarp, wood supplies, and food and water dishes) ran me about $175 - which is more than the $150 I had planned to spend on cages at the farm store. I figure it's alright though because it's a good investment. I can pull this enclosure down when I don't need it anymore and it will store a lot easier than five assembled wire cages would..
After watching them for a while, a few things became apparent. First off, Carswell is definitely a dominant buck. He will pick a fight with any other buck he comes across and make sure they know he's the boss. His only adversary that really put him in his place was Thumper - who was immediately returned to his separate cage (NOTE: I wouldn't usually throw bucks together, but Carswell and Thumper have been in side-by-side cages and have not shown any aggression, marking, or dominance thumping behavior, so I thought I'd try).
Second, I noticed that Bertram was never bated into fighting. When the other bunnies started to scuffle, he remained calm. He made no effort to fight or run away, and after one or two attempts to instigate, Carswell gave up and left him alone.
Third, with 25 square feet of space, it took about 45 minutes to an hour for everyone to work out their differences and start to get along - this being largely Carswell causing issues. I think the true saving grace here is that in the afternoon Carswell was removed from the cage and moved to his new home (where he will be a meat breeding buck). Now it's just the three that have been hanging out together at the resort anyway, which seems to help greatly. I will continue to monitor closely for any signs of aggression - as bucks are known to fight and I don't want any issues here. Worst case scenario, I do have a few odd cages that I can house them in inside the kennel cage to keep them separate if I need to - I just don't have stands or roofs on those cages.