Shorelander trailers have a little different seal size than standard and an additional spindle sleeve that slips over the area of the spindle that the seal rides on so that it is a smooth surface. I think if I recall when I changed my bearings I replaced the spindle sleeves as well. If you were on the side of the road in a pinch im sure you could leave them. My trailer is a SLR23SW. Here are some of the part numbers I had looked up a few years ago. Not sure where you are located but I was able to just go to a local shorelander dealer (Dan’s South Side Marine) and get the spindle sleeve and seals
4470400, HUB 1 3/8 X 1 1/16 CAST
4410089, SPINDLE SLEEVE 1 3/8-1 1/16
4410130, SEAL 1 3/8IN
For a spare hub what I did was order the following since it came without grease and then packed it with my preferred grease (red n tacky) and installed the correct shorelander seal on it. Have not had to use it since its a spare and hopefully never will! These come with cheap chines bearings, but for a spare it probably does not matter. You should be able to buy timkin bearings from rock auto or amazon for pretty cheap as well.