That's exactly how I did mine when I bought my boat a couple months ago. I deal with 12 volt wiring very, very often and the by at least a 10-1 margin, grounding problems are usually the culprit when lights don't work, or flicker, or burn dimly, or..... I didn't use Harbor Freight lights, but I did use the exact same technique of installing them as you did.
I own a semi trailer repair shop, and we also install dump beds and poultry litter beds on trucks. We do A LOT of light work. My guys hated me when I locked up the butt splices and got a couple small torches, solder and shrink wrap. We can't alway run a continuous ground when repairing old stuff but on any new install, we run a continuous ground. It is even more important with the LED lights.