As far as kind of grease, make sure it is a "wheel bearing" grease, of which the choise is yours. I dont see a big difference in quality between the major brands, especially for a "pop-up" camper which would probably be used seasonally, and doesnt carry heavy loads. Regular grease, for ball joints and chassis lubrication, etc. will not work for wheel bearings. It has to be wheel bearing grease.
As far as packing a bearing with grease, there are tools, mentioned by the other posters, which work great, but require an initial investement. If you just have two wheels to do on your "pop-up", and will do no more, you can load your bearings by hand with grease. This is a fun job. With clean hands just take a "golfball" size glob of grease in your left palm (if you are right-handed) and "rake" your bearing, bigger side down, onto the edge of the "glob", forcing grease into the inside of the bearing. Keep doing this until the grease is coming out the top of the bearing. Turn bearing slightly and repeat, until you go all the way around. Then glob grease over and all around the bearing. Keep it as clean as you can.
