my 78dode american clipper won't start

hello I'm new to the RV world I was just given a 1978 Dodge American clipper and I love it. 1 thing tho it was sitting since 2016 and I'm having sun troubles with it..... first off it won't start I've had it going a couple times but honestly I'm not to mechanically inclined ...... so far I've changed the coil and starter and put a brand new battery. so yesterday it died on me while in gear still I had my friend come give it a jump went to the gas station and it died again. not to sure  and I could take use sum help plz