Rich,
I installed electric brakes on my older steerable Demco dolly. The only problem that I had was that the spindle mounting plate was at a 45 degree angle. I did have problems with that since the magnet was not at the bottom. I was told by Dexter engineers that it would be OK to mount them at the 4 o'clock position. Not true in my case, constant problems until one day the brake froze up and a blowout occurred. I had the plates removed and re-welded by a trailer repair facility and since have had no problems with them.
I thought about going with disc brakes, but decided against them due to the fact that I would have to buy an actuator for them and I was already set up to tow with electric brakes. JMO