Hi..I weight train 4 times a week and do some cardio also. I've done this for the last few years and have been T1 for 4 years....I have put about a stone on although my aim has been to stay in good shape, not necessarily bulk up. Anyway, I am in very good shape so I know what works for me, can't guarantee what would work for you. I train at 6.30am-7.30am without eating beforehand...I then have some tinned fish and a piece of fruit and some nuts of any sort with a small amount of insulin...for lunch I'll have wholemeal sandwich and some more fruit with some insulin. I eat whatever my wife makes for evening meal...if I snack it's usually some packet chicken etc...so no carbs really.
Dont eat junk though, that'll do you no good....just try to eat plenty of protein...and enough good carbs.... The other hugely important factor is what you actually do in the gym. If you have no idea of what a good workout looks like then it makes no difference what you eat, you'll never really get in decent shape.
Also you obviously need carbs but it dont think you cant low-carb. I eat next to no carbs really and for that reason my insulin use is low...I have 3 units with breakfast, 6 with lunch and about 4 with evening meal...and I'm 35 years old and 12 stone but all muscle. You only need carbs to combat a hypo if your insulin use was too high to begin with...get that right and you can eat low carbs..happy to share anything else with you if you need.