Usually just the measurements are all that's required which a $10 set of digital calipers will tell you. I do a lot of trailer service for a local charity and after a while you begin to recognize the measurements and where your most likely to locally source them without relying on the expertise of the parts pushers behind the counter or trying to match a bearing by an exact make or model.
On the seal all you really need to know is the ID, OD and how thick. On the bearings its the same along with how many lbs capacity the axle is and if you want high speed which of course you do.
Very important too is to use the correct grease and not to mix and match without checking the compatibility chart since many are highly incompatible with one another and will turn from grease to grit when the pressure additives in two incompatible grease formulations adversely react to one another.
2001 Winnebago Adventurer WFG35U