I would say your proseal workmanship is acceptable. There is a lot of archived threads on proseal techniques that you should read through, here's one of the best:
Rick also posted a workmanship standard reprinted from the manufacturer's data which I can't find at the moment, but have a look for it, it has diagrams of acceptable techniques.
I couldn't justify buying a Semco gun to apply proseal, but I think if I did I would have loved the tool. In its absence I made a "poor man's Semco gun" using some large syringes I bought at the local farm/feed store, and some pieces of 3/8" aluminum tubing (the 3003 stuff supplied with the kit). I made a number of curved nozzles and shaped the nozzle ends to look like some of the Semco nozzles on their website. Worked very well and I recommend that you experiment with this type of application.
I too used almost a quart of proseal per tank. Every joint was prosealed as well as every rivet shop head and a fillet on both sides of each joint. This was taken from the manufacturer's workmanship manual.