Most if not all states require continuous brakes. Some require brakes for
trailers as low as 1000#.
Ask the U-Haul dealer if the truck has a brake controller, and if it doesn't,
ask if you can install yours. Most require wires only to the battery + & -
and the stop light switch. Your blue wire (preferably 8 ga., min. 10 ga.) to
the trailer brakes can run straight from the controller to your trailer brakes
without a connector since you will not be disconnecting until you drop the
trailer at its destination.
No modifications to the truck will be necessary. If you can't find a hole in
the firewall to run the power wires thru you can run them out the door jamb
and dive them under the edge of the hood to the battery. The brake wire can
go out the door and be tied to the frame on the way back to the rear. The
stop light switch wire can probably be held to the spade lug on the stop
light switch by the factory connector. An alligator clip can be used.
If the U-Haul doesn't have a receiver you won't be able to use a WD hitch,
but unless the U-Haul is a really small one its hitch should be sufficient. I
towed a '52 Spartanette (7800# listed weight) with a midsize U-Haul a few
years ago. S-l-o-o-o-w. Not any 45 mph; 20-25 max.
Your trailer (most likely) uses a 2 5/16" coupler; the truck probably has a
2" ball. You will have to swap yout 2 5/16" ball for the trip and then swap
theirs back when done.
Al Grayson