Big litter woes! On vacation!

Hey y'all! I know I haven't been around the forums in quite awhile... I've been really busy with my 5th/last year of school lately! But I've got quite a big problem on my hands today! Oliver and I are visiting my parents for Thanksgiving until Sunday... well my mom went out and bought a litter box (same as the one he already has) and litter to keep at their house so I don't have to bring his back and forth... well she bought Nature's Miracle litter (not what I usually use) and I didn't think anything of it. We set up his box and put it where it always goes when we're here... I checked just now, and he hasnt used his box! (We got here yesterday around 3pm) I had purchased one of those disposable plastic litter boxes with clay litter included for the car ride, so I just ran to my car and got that and he peed right away, but the box isn't quite big enough for him to be comfortable in.... well, I took some of the litter from the disposable box and put it on top of the nature's miracle in his big box and also scooped his pee clump from the disposable box into his big box... I'd like to get him used to the nature's miracle for when we visit my parents (plus, I don't want my mom to have wasted a good amount of money).... any other suggestions?!?! Should I spray some feliway in his big box with the natures miracle or would that deter him from peeing there? I did put him inside the box and he stood there looking so confused and jumped out! We're heading out for Thanksgiving, but I'm leaving the disposable box available to him while we're gone... I don't want to pour all of that litter into the big box for fear that he won't use it....

Ok, so of course right after I type this "OMG help!" thread, the stinker has to poop... he started digging a little in the disposable pan, realized it's not big enough to be comfortable and hopped in the big box and pooed! I praised and petted him when he was done.... I'm still gonna leave the disposable box available while we're at dinner just in case.... suggestions are still welcome though, haha

Do you think we worry too much and cats do what comes natural? *
Your cat is lovely btw.

Thanks for the compliment on Oliver! So many people gawk over how handsome he is... not bad for a street kitty

We started my kitten out in a disposable aluminum pan and he didn't like the bigger box either. I put the disposable pan inside the big box and it caught any overflow. Clean up is easy too.