How do i show him i care?

my dad is under a lot of stress with his job and to top it off where going camping with his girl friend and her family. we don't have a camper yet and its next weekend. that has him very stressed out. theres gunna be 8 of us ( me, my dad, his gf, and her 3 children, and my brother, and his gf.) and if we get a pop up i feel like he has to make her feel comfortable and know that her family is safe and comfortable ( which i understand) but i feel like im gunna be the left out so to speak. because me and my dad went to Florida with his gf and family and i had to sleep on a cot for a week and i don't want that to happen again. plus she has a nine yr old daughter and i don't like her at all. but i don't hate her she just really spoiled. anyway i told this to him and he got the idea that im not supporting him and that know one is and he's the one telling me to be honest but i feel like when i do i say the wrong thing so i don't usually say anything ( my personal motto is " i give for the enjoyment of others." and i tried to apologizes for what i said and he got more upset. and i fell very bad. and i want him to know that i love him and iv got his back maybe not financially but mentally and emotionally. and im very proud of him and all that he does for my family. i just don't know how to show him without saying the wrong thing.