I don't 'Roll' anything anymore.
I discovered a $13 Shutz undercoating gun, and I haven't had to deal with the mess of a roller since then!
I use Herculiner.
It's the best of the 'Cheap' self-applied coatings.
Goes on easy, repairs easy,
A little sensitive to UV light, so you have to freshen it up every 4 or 5 years if you don't have a top on...
Cuts with Xylene paint solvent, so you can wash down with Xylene and spray new top coat or repair coat with no issues.
Air powered spray gun is the absolutely best way to get the stuff on.
you can do an entire interior of a tub in about 10 minutes, and you can get into places you can't hope to reach with brush or roller!
Keeps YOU a lot cleaner also!
I get the 'Shutz' brand undercoating guns off of E-bay for between $10 & $20, and they save you a TON of time, money & cleanup in the long run!
On a warm, humid day you can litterally make Circles around the tub, and finish up one 'Lap' aorund about the time the stuff is ready for the second coat,
Same for the third coat, and you are done in one setting instead of having to go back over and over and over again!
NEVER DO ONE COAT,
You need a MINIMUM of two, and get the best results with 3 or 4 coats.
That's 3 or 4 seriously sticky messes if you use brush or roller!
Undercoating gun lets you keep the particles of rubber suspended and distributed better than with a brush/roller also,
MUCH LESS WASTE of product that is $75 for three quarts in a gallon can...
I usually use one of the sand blaster guns that have a suction tube to a bucket for seams, rust spots, feathering down where paint has chipped, and removing paint that isn't adhered well.
They come off the tool sale trucks or E-bay for $20 or so also.
If you get the Herculiner spray gun kit, it's just a sand blaster gun, and they plug up when you shoot bedliner through them.
The Shutz guns do a much better job.
If you get the stuff with rubber particles in it 'Rough',
Then there is no such thing as too much stirring, and the gun will let you lay on the liner before the rubber particles drop out of suspension.
Can't do that with a brush/roller, you have to stir constantly and you still won't get as even of coverage as you get with a gun...