Seems like if you could pick up a used smaller semi-tractor with a sleeper, you could do OK. It would pull just about anything and no need for hotels (which I suspect is the big money loser if you have 5 nights at $100/night).
So if your example run grossed $1950:
- 3000miles at a 10mpg average (you should do better returning empty), that's going to be 300gal...lets say $900 in fuel.
- $50 towards insurance.
That's netting you about $1000/week working 5 days a week or about $50k/yr. Let's say you put $20k/yr aside for maintenance and buying a replacement truck that's $30k/yr or about $15/hr.
No you aren't going to get rich but it's some nice extra money and if you can find a few return loads, the hourly rate goes up substantially.
If you own the truck anyway to tow your RV, you can ignore most of the depreciation (or benefit from it tax wise) and reassign some of that $20k/yr to net profit raising your hourly rate.
As a part timer, can you pick and choose runs at all? If you aren't pressured to take every run that's available, you could take runs to destinations that interest you and expense all the travel cost and then you are there with your mini-RV for a week or two.