gfbishop,
If I were planning on towing a multi-horse trailer, I would be looking at a specially ordered rig with horses in-mind.
The company that built our rig will strengthen the frame extension to accommodate a heavier tow condition. They also will build upon request, their short E350-V10 rigs on an E450-V10 chassis. I understand that both upgrades are charged at cost.
You would rest well with a shorter lighter weighted motor home with the stronger frame & brakes of an E450-V10, and a special frame extension & hitch for your multi-horse trailer.
I feel that when it comes to horses, you need to add a lot of extra margin over what the average motor home can offer. It's not just the weight alone, but potentially unstable shifting weight. I suppose if your horse towing travels remain local, you could get by with less. But if traveling the country, I recommend a setup with that extra margin. Traveling the country will present you with all kinds of road conditions where the extra margin will help keep everyone and everything safe.
