As a rule you should always follow, NEVER connected anything to the battery without a fuse. Absolutely NOTHING.
Yes crimped wires are much better in a moving vehicle.
Soldered wires create a stress point that can cause the wire to eventually fail near the solder joint due to the vehicles motion and vibrations.
Always use stranded wire in a vehicle, never use solid house style AC wire for your 120VAC circuits. Solid wire is not designed to withstand the vibration and motion of a moving vehicle and will eventually fail.