I have to question what $1,500 covers, there are a lot of hidden expenses in RV ownership, though some of those expenses would exist if one were living in an RV or not. Lets assume someone is talking about living and traveling in a motorhome, as cost of travel trailer gets more complicated given the addition of a tow vehicle most people don't already own.
First we have the cost of the motorhome, with a bit of shopping one can find a used motorhome that has been well maintained, is not rotting to pieces, and is not so old as to be considered an antique for around $20,000, maybe $15,000 if you are lucky, though on average the less you pay the more things that will tend to need maintenance and repair. I paid a bit over $20,000 for my 2002 Safari Trek in 2016, and have since put something over $12,000 into it in maintenance, with probably another $4,500 planned in the next 12 months, doing a fair amount of the work myself. Though I admit a lot of the stuff has been optional upgrades, such as adding GPS nav system, TPMS (tire pressure monitors), but there has also been a fair amount of necessary stuff, alternator, fan clutch, failed automatic parking brake switches, and some stuff in between like, new shock absorbers, new front ball joints, and coil springs, sway bar bushings, ...
Upcoming repairs are going to include getting the dash air conditioner fixed (estimated at $1,700), new tires as mine are aging out at about $2,200 (good off brand tire), ....
So lets work from the numbers I have for my coach, which gets used about 75 days per year on average.
I financed it over 4 years with payments under $500 per month, lets assume with current low interest rates someone were to finance over 8-10 years, a reasonably life expectancy for a coach that is now 15 years old if continued to be maintained, we could hope to lower the monthly note to around $250-$300 per month. Amortize in the typical replacement cycle on longer term items like tires, refrigerator, air conditioner, batteries, etc. which we can safely bet will average another $200 minimum over time (there is a reason that the 15 year old $20,000 motorhome sold for $100,000 when it was new). So before we even get to insurance, fuel, oil changes, roadside assistance plans, we are already looking at something on the order of $500 per month. Then comes travel cost, I generally calculate my cost of travel at about 35 cents per mile, which is probably low as it does not take into account drivetrain wear, and of course then you have cost of a place to stay, campgrounds are not free, and there is only so long you can camp out in the middle of nowhere on federal land.