I own a Ford Ranger and want to know whether to pack extra grease in the hub, especially in the space between the inside bearing and the seal and within the spindle cap outside the outer bearing. I have heard some of the same arguments on each side.
I would not recommend packing either the cap or the space between the bearings. The external cap is only a dust cap and is not meant to hold back grease, just keep the dust out. The story is very similar with the inside seal. The seal is just to keep the dust out. If too much grease is put in, it may get displaced and get past the seals making a mess all over the brakes. That being said a little extra grease should not hurt anything.
High quality grease should always be used and a bearing packing tool is recommended. Apply some grease to the races before installing the bearings. Also place just a little grease on the surface where the the seal will ride.
Packing the free space in the hub will do very little, if any good. In normal operation the grease doesn't flow, so the extra grease never gets anywhere near the bearings. The grease you need and want is the grease that "packs" the bearing – filling the spaces around the rollers. The easy way to get this in is with a packing tool, there are several varieties. Here are two from Lisle that are relatively inexpensive.
They both work by forcing grease through the bearing to surround the rollers, one uses a grease gun, the other uses a built in reservoir of grease.
This video shows how they work.