I can't think of anything that may be comfortable enough to rusty. Wearing a dog kangaroo for too long may cause him injuries and keeping him in a cart with little space to move may discomfort him too. HOw about a foldable stair he can climb?
He needs to stay in contact with other dogs. At first you have to find friendly adult dogs to socialize with him, but you must always be near him so he feels safe and protected. AS his trust in other dogs grows slowly, find other friendly dogs to ex…
I have used FRontline and Revolution. Both work just fine, never caused any skin or toxic reaction on any of my dogs and I dare say frontline is even stronger as a repellent than revolution. Revolution tag says it can be used even in nursing females.