You did not include info about which data loggers you were looking at. However, I would suggest you deal directly with the manufacturers rather than third party sellers. So I would suggest you contact Onset Computer for their Hobo loggers. I suggest the UX100-003 logger. It does T and RH and is reasonably priced. The software for the loggers is also important, so don't discount its capabilities in your decision. In my opinion, the Hobo is the best overall combination - not the least or most expensive logger, but the best for the money. You really would be better off talking with a qualified conservator rather than trying to get this info off of Museum-L. A conversation is much faster than all of this typing.