I would say the best thing for them to do as good will and standing behind their product is to send you a complete new trailer, and they take this one back and fix it..
Probably not. But fix it they should.
Warranty claims usually don't include the cost of shipping the goods back and forth. On a small item thats usually not to much of an issue, and its often shared by both parties (one each way). On something like a CT, well thats going to be an expensive procedure.
Without knowing the full history of this saga. The truth of the matter is, that regardless of the truth; both parties have to find some common ground. It doesn't matter how they communicate, email or phone, just do it. Email isn't so bad, as everything is in writing. Telephone conversations can get a bit "he said she said".
How hard would it be to remove the tent section completely from the trailer and send it back to MDC for repair or replacement ? It would certainly be a far cheaper option than trying to ship the whole box and dice.
On the mattress front. I believe the manufacturer has offered to reimburse the customer for the cost of a mattress. That to me is fair and reasonable.
My advice would be to pick up the phone and talk it out (reasonably). Come to an agreement, then have the supplier put it in writing by sending a email. The customer replies by email accepting the offer. Then get on with fixing the problem.
If either party is unwilling to negotiate a fair outcome, take it to the relevant authorities for mediation.
Regardless of whether or not MDC are doing the right thing (legally and morally) or not, this issue has become more of a public relations exercise. Maybe they just have to take their lumps on this one, bite the bullet and realise that to make this problem go away will cost money.