I originally had the manual "boat buckles" tie downs for my boat and never had them loosen off. Make sure you crank the bow of the boat up tight against the bow roller. I've since switched over to the retractable ones and they are very convenient and in my opinion worth the money.
The first year I owned my boat, I also experienced carpet wear on the bunks. I learned it was from the trailer flexing while towing. I just took my old tie down strap and modified it a bit and use it as a bow tie down. The bow is now snug to the trailer and I no longer have premature wear on the bunks.
Here is a picture (not the best pic)
BPS also sells the bow tie downs.
These are the marine batteries available at Costco,
Group 24, deep cycle, 685 MCA, 95 AH, $77.99
Group 27, deep cycle, 750 MCA, 115 AH, $89.99
Group 27, starting/deep cycle, 845 MCA, 120 AH, $99.99