Litter Box Issue

I brought my 2 ferals inside that I've been taking care of for 5 years. B started using the litter box right away. F has decided that he will only go on my spare bed which is now covered in cardboard moving boxes and paper. I have tried Feline Pine, clay litter, and every litter in between as well as pee pads on the bed and in litter boxes. Any helpful hints on how to get Flash to use a litter box? I do not have lids on them. F scratches and meows at the door for 5-10 minutes then resorts to the bed and trying to cover it up for another 10 mins. He doesn't like to go there and I can tell feels guilty each time he uses the bed area. I have to move them 5 hours away in 3 days in addition to a visit to the vet right before driving. Definitely don't want to let them outside and want to do it right when I get to IN. Help! Thanks all.

Try some dirt in the box- he is used to going outside that maybe dirt will make him feel more comfortable with the feel and smell

I am so glad you got them inside and they are doing ok (other than the litter issue).  Maybe try using some Litter Attract.  You can get it at pet stores like Petco.  Also, maybe he has a UTI?  The vet visit will let you know if that is the issue.  Best of luck!

I've found Dr. Elsey's Cat Attract litter has worked well for my ferals in the past. Also using a larger, shallower litter box like an under-the-bed style storage bin from Sterilite or Rubbermaid often appeals more to ferals than the smaller "official" litter boxes you get at pet stores:

Thank you for all the suggestions. The Cat Attract litter attract is what worked for B but not for F. I've tried dirt mixed with litter, dirt only, dirt covered with grass, and none of those have worked. I'll try the large shallow box next.