It is hard, I have a 4 and a half and 2 and a half year old right now( So I have been in your shoes), and my Dh is a full time worker, and is currently spending 3 nights a week at him mom's house, helping with his adopted special needs niece and nephew, as my FIL has cancer. I understand, like you, that what he is doing is right and important, but, yes, it sucks to feel like me and the kids are moved to the back burner.
I am reading a book right now, that I got from the library, by Dr. Kevin Leman, called "7 things he will never tell you , but you need to know" all about how men think SO differently than women, and why we definitely don't "get it" about each other, lots of times. If you get it and read it it will help you understand where he is coming form , onte man side of thing s- everything to themis a competition/conquest.....sound slike he has already "conquered" getting married, so now he is on to conquering school and career. Guys don't really understand the ongoing maintenance part of things...or them emotional relationship we have to our kids - that if he physically cared for them more, gave us more of a break, that to us is like foreplay, LOL.
Good luck, it is an on going battle trying to communicate to them so it is recieved correctly, and trying to keep our own sanity.
Maybe you need to get a baby sitter one night a week EVERY week, and then alternating weeks, - you go out by yourself or with a girlfriend and then the opposite week, have a real date with your husband. I am great one to talk, we don't do that, though I know we need to. I do have my own hobbies, and I do make time to do them - I crochet and I create things from Polymer clay. I just spent a couple hours last night cleaning up my craft room, so i can start in with full tilt production a few nights a week, and I am going to start an Etsy shop with my creations.
Do tell him you'd love to go camping when it is warmer and more pleasant for you and the kids, but timing is going to be bad with the weather reports. Explain all that will go into it with the kids, and they they will probably be fussy or whiney all the time, so he will understand that it would probably be better to do this when weather is better, with them still so little. Suggest some other activities for next week that will be warmer/easier/more pleasant - including a baby sitter and adate time for the 2 of you.
Yes, it is so easy to lose ourselves in "mom" mode and get so frustrated. We have to work our way back and we have ot make our marriage a priority, even in thes rough baby years, because some day those kids will be gone, and if we don't stay connected to our spouse, we won't even know them any more, and things will fall apart when the kids ( the focus of our relationships) go away.
Keep working on it - I am and it is a work in progress!
Jessie