I had one a long time ago and it didn't work out.
Instead I took a bike rack (am assuming your dirt bike is of the pedalling variety) and mounted it to front of the trailer. Steps were:
*Welded a length of metal tubing, slightly larger than the bike rack's tubing vertically center of the trailer's front frame.
*Cut the "goose neck" off the bottom of the rack and pushed it into the new tubing.
*Mounted the bike and I was set to go.
Oh, I did drill a hole completely through the new tubing and the rack and inserted a pin through to remove the possibility of bike and rack hitting a bump and flying off.
YNCM USN-Retired (64-90)
RVN (Tet 68)
2015 Thor Vegas 24.1