Mine is not built exactly like this but after I got mine built I realized how it could have been simpler.
You will need a cheap dollar store 12 air pump, enough cheap water hose for the length of the boom. a container 5 gal that will be able to be pressurized. a valve stem and a Galvanized T that can be screwed in to the container . I used a plastic jug but as soon as I can find a old metal can (like bravo used to come in ) that has 2 bungs I will change it out.
Drill a hole on the low outside of the container for you to insert the valve stem. remove valve and use a piece if wire to feed it to the hole. Most of 12v air pumps have a locking chuck on it that will clamp on the valve stem. Air supply is done
screw a T into the small hole of the can and you will need to get a threaded hose bib to connect the hoses. zip tie them to the boom . a 20oz soda bottle taped to the end of the hose helps it drop clumps of foam.
you will have to add extra wire to the pump to it can be connected to the battery.
fill the can with water and get the Cheap CAR WASH soap 32oz(I think) and put about 1/2 of it in the can and screwin the big bung.
turn it on and the only place the foam can go if everything is seal is out the water hose.
mine drops clumps every 20-25ft I refill the water and add more soap about every 12 acres.