Smokey and the Bandit Truck and Trailer Replica

[frizzen]

If i didn't know better, with all the necro posts i'd think you really wanted to build a Snowman outfit...

You can fit smaller 2S lipos that have similar or better Ah ratings than the stick packs these were designed for.
There are other options than the MFU that might fit your needs
You could swap the 3speed for a straight gear reduction, or even a 2-spd to gain more room under the body.

Check out some of the Day Cab builds that are full of options. If they can do it, tiny sleeper shouldn't hold you back too much