Need a bigger car.

My husband and I are expecting our first due in October. We have a truck and I love it, it's 4x4 black on black lifted it's awesome. BUT it's a single cab. We both know we need a bigger truck/car for when the baby comes but we can't afford getting another payment. I feel so bad because it's his first car and he was able to get a good deal on it and start paying it on his own at 18 years old. When we talk about it I always suggest he trade it in for another truck that's 4 doors and we can always fix it up later. He agrees at first but then says that's his first and he wants to be able to go on rides with our son and take him mudding and all when hes older. How can I convince him we need to trade it in? Our son is very very important to him but it's his first car and I totally understand why it's hard for him to let it go so please don't come on here being rude.