Well I wouldn't really trust casters on a rig anyway, locking or not. Maybe on a rig that where the seat and stand are connected, but I'd just anticipate that moving around, even when locked. It looks like those aren't meant for that stand anyway, but you could probably make it work with a little drilling. But again, I wouldn't go that route.
But really, if moving 45 pounds around is giving you back pains, that sounds like something you need to address. 45 pounds... really isn't that heavy, assuming you don't have some sort of physical disability or are elderly. Make sure you're lifting with proper technique. Maybe incorporate some stretching and exercise into your daily routine. Maybe even take up some light weightlifting. You'll be better off for it in the long run, and you'll feel stronger, healthier, more capable, and generally just feel better overall.
But in the meantime, you might try a furniture dolly like THIS . You'll still need to lift it up on there to move it to where you store it, but at least you won't be carrying it.
If your concerned with space try looking up Mini ITX builds and just buy a 24" 144hz monitor.
You can build a 3070 Mini ITX Build with an 8 core Ryzen and 32 gigs of 3600+ mhz speed ram and 2tb nvme SSD for under 1300$ that outperforms a 3080 laptop that costs over 2000$
If you need it to be movable at a moments notice then just buy a small dolly like this and place it on there. Wireless keyboard,mouse, and headset like the hyper x cloud flights and you'll be set!