Usually you can find weight of the camper by searching for the model and "weight", i.e. "Lance 915 weight".
For a lot of campers, especially Lance, the manufacturer has old brochures available for download which will still have the specs. Just remember weights in brochures are without any options so can be 500# off.
On the camper there is a tag which will list the wet weight. Sometimes they are hard to read, but most times they can be read enough to get a could ball park.
Quick rule of thumb I use is 8'-9' should be about 2,000#, 9'-10' should be 3,000# and 10'-11' should be 4,000#. However, there are some brands that are very heavy where a 9' camper could be pushing 3,500#.
I agree, with above, if you have kids, plan on at least a SRW 4 door truck. The fuel mileage lost for the extra space won't even be noticed.
Unless you are really needing to tow something, for better all around fuel mileage along with more space, you may really want to consider a travel trailer. With an F150/1500 you can tow up to about a 30' TT yet get decent mileage when empty. This also works better if your camping method is go someplace and sit for a few days before heading home. The TC advantage is towing or moving about a lot.