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Tent or no tent, once they can climb out they are in danger of hurting themselves. Dump the tent and go through the transition. Yes! You will have to deal with weeks or more of quietly walking him back to his new bed,perhaps repeatedly for some nights. It's not fun but it must be done sometime. Why keep him penned in?
I've posted this here so many times but here goes again: Friend's 18-month-old fell the FIRST time she tried to climb out of the crib and broke her arm. If she had landed on her head or neck she could have been paralyzed or killed. I always say: Put up the crib rail, and look at the distance from the top of the raised rail to the floor. Imagine a small child falling that distance head first.
Put him in a mattress on the floor and save the toddler bed expense, and just get ready to work with him on staying in bed. It's another phase of training him and has to happen at some point. If he can climb out of the crib and is as you say "a major marauder," don't you expect soon he'll try to take off or fight the tent?He could get entangled in it. He's telliing you he's ready for the transition.