So, there's a Grand Design Momentum plan with a front living room, but it won't have room for your Miata in the "garage" as the garage in that one is more meant for a motorcycle. I feel like I've seen one other front living room model ever, but I can't remember what it was! None of these are less than 32' though. As I'm sure you've already discovered, finding a 5th wheel trailer with a 13' garage but only 32' is going to be a challenge, if not impossible.
Heartland Cyclones have a few unique floor plans (like a front bath), but none of those will have a 13' garage.