Yes, you will get mixed answers because I went through the same thing. I have, for 30 years, brought at least 10lbs back every time I visited RP. When asked what I was bringing back, I said shrimp. I was never asked how much. On my last trip I wanted to bring back about 25lbs. So I started checking.
Some say 50lbs and some say 5lbs. I was told the amount is determined by the county where the border crossing is located. Lukeville is in Pima County and if you call Pima County offices, they will tell you 5lbs.
I think you will be fine. Just put it in the ice chest with the ice on top of it. No one at the border is going to dig it out and weigh it. :)