Dog Box Doors- Help!

I bought a 4x8 enclosed trailer that I am converting into a rolling dog box. Mostly because one of my dogs is a Dane, but also because I have too many dang dogs! I am trying to figure out who makes dog box doors big enough for his big butt to fit through. Has to be at least 30 inches tall- biggest I find is 21 inches.

Does anyone have a lead on who makes a bigger door? I am thinking like the big ones on the sides of animal control trucks would be about perfect.

I will post some before and after pictures of the trailer project when I get it done- it's gonna be sweet.

thanks!


Current dog count:
Cash- Great Dane, blood trailing and coon dog
Tucker- Aussie, cattle dog
Trooper- Aussie, resident bad [censored] (she does it all but is 14 so now she just watches)
Jake- Aussie, Cattle
Zeus- Aussie/catahoula mix FOSTER DOG! Up for adoption soon- started on blood trailing.
Rose- Blue Lacy- the other resident bad [censored]- 8 years old and still does everything the other dogs do and better
Creek- Blue Lacy puppy- Being trained for blood trailing and hogs