i am not a fan of rubber caster wheels when there is a good amount of weight involved. make sure ya go with metal caster wheels. rubber wheels, i have had them catch, and bend side ways on me, to simply cracking. there is pure metal wheels, and then a metal wheel with a little say 1/8" bit of rubber around the outside of the wheels. if you want to keep from scratching up concrete floor.
be mine full of what happens if hydraulics begin to leak down... it could cause bucket, boom, etc... to fold right off dolly, (edge of were bucket is) or fold off in opposite direction.
out riggers do and will collapse to the ground. and it may only be one or other or both that drop at different rates to the ground, and could possibly tip everything over.
also don't rely on out riggers to keep backhoe from falling over when on the dolly, they can and will leak, possibly causing backhoe to tip over.
google...
backhoe dolly site:
www. tractorbynet .com
((added 2 spaces to above link notation due to forum software automatically coverts it to something else))
and then i just googled
backhoe dolly
then clicked up on images and found below videos
https://www.youtube.com/watch?v=5-2vmslLBVY
https://www.youtube.com/watch?v=dRNO35pwUkE
most of the images i saw, everything kinda folded towards the center, though i did see a few pictures were... bucket cylinder could leak down some causing dip stick and boom to all fold over the bucket and make things fall off the dolly.
in one of the videos it looks like guy is using a dog leash (a clip on each end) to hold out riggers up. looks like the rope is fairly tight most likely a good thing.