Digital converter box

My son Evan does not have this mitsubishi dtv yet. He is using a VCR as a converter box hooked up to a factory installed DVD player in our mini van. He an pull in television stations on this, but the picture is very week. He now want to buy a digital tv tuner converter box to try to get a better picture and because tv in going digital. We live in rural Montana and can not get very good TV signal anyway. We also don't travel that much. We are however going on a trip this summer, but it will probably be another year before we travel more than 250 miles from home. Will hooking up a digital converter box make any difference. Will the electronics and electricity in my mini van handle all of the items.
Thanks,
Kathy, Evan's mom