Always pays to physically check............ bearings best check whats fitted a pain to check, I did with mine then found that Big Mals maintenance book listed them, mine are parrelel so same bearing on outer as inner, my bearings are the same ones it came with, so they have done over 80K km, always checked after each trip and greased up once a year as I give the brakes a clean, not a biggy as my vehicles run near 300K km without a change and sometimes not even a grease..... Regular maintenance is the key as you know..... and its a bluddy pain but pays off...................... I think I have old spares of Holden and Ford bearings, all greased up and still sealed in their vac sealed bags......... have no idea what my boat trailer bearings are but have them covered I think.........
Don't forget to carry a spanner that fits the hub nut and a split pin, or a 3" nail, coat hanger wire works as well. I have a huge metric adjustable, covers many tasks.... Why have mine lasted, I pack the hub enough so if water gets in theres not a lot and I have taken to using marine bearing grease, when I have removed and greased them I go for a spin around the block then jack up and give them a shake, something I hate doing but force myself to do it, otherwise that will be the time one is loose.......... Murphys Law is proven to lay i wait for me..........
Those new tyres will be 10mm higher, 30mm wider which will mean the sidewall will be 15mm closer to the inner part of the guard/chassis, which is usually okay... hope they are LTs as if they are P rate you might be running close to max pressure... going by my slide rule.