Frustrated with husbands job which in turn is causing tension

Just need to vent. Before I post I am beyond grateful that my husband has a job, before I get the comments about that. My husband leaves at 7am and usually doesn't return until 7pm or after (he drives to different sites all across the state including 2 other states). He is typically only supposed to work until 4:30, but does overtime(again don't mind). The only problem is we have 2 young children ( 5 years and 7 months) that miss him and when he comes home he's grouchy(which I understand, but our girls and I miss him). His job doesn't pay him enough for this. He does triple the amount of work for $15 an hr. He has been given bumps up in positions, but no raise. Now we are planning a family vacation, but it's so much better to go in February with pricing. He has the time and he would be out of work for 3 days one week and 1 day the next week. His work is denying him because they "may be busy" that week. They book my husband 2 weeks advance, so giving a 4 month advanced notice should give them plenty of time to work the schedule. If we go at the time in March, which we have planned at the moment, it close to $1000 more. He is aggravated with me for being upset about this, but I just feel his job takes advantage of him. He even worked for them while our daughter was in the NICU, on weekends, early, overtime, and he has done other positions for them when he is not required to. I seriously can't stand his job. Grateful for it yes, happy with it...no.