Unfortunately, moving your assets into an LLC or another person's name will not necessarily protect them from an IRS levy.
Even if the assets were transferred before the IRS filed the intent to levy, they may still be able to go after them as well because the IRS sees it that you made this person, corporation, or trust the nominee for this asset and they will still be able to pursue this asset. This may slow the IRS down from taking assets and can buy you some extra time to set up an agreement with the IRS to release a levy, but it will not eliminate them from going after the asset entirely.
On some assets, if you can prove to the IRS that the asset they are trying to seize would not be worth it for them to seize then the item can be claimed as exempt and the IRS will no longer go after that certain asset. Typically, you will have to prove that the effort it would take to sell the asset would actually cost more than the asset would eventually sell for. You can also get an asset to be claimed as exempt if you are able to show that the asset will prevent you from working. Many times the IRS may try to seize assets such as cars, trucks, tractors, etc, that may be required for you to do your job and earn money. If you can show the IRS collector that this asset is required for you to earn money, it is likely that you can get an exemption on that asset.
An LLC is a good tool to put an extra legal layer between you and general creditors, but it has no effect on stopping the IRS in going after your assets. You should instead try to find other ways to keep the assets such as claiming them as business necessities, etc.
I am sorry not to have responded sooner to your last question, but I was not in the forum at all yesterday.
As far as your boat is concerned, regardless of whether or not it is used as your primary residence, the IRS may still place a lien on the property. With a lien, if you tried to sell the boat, the proceeds of the sale would first be paid in full to the IRS.
The IRS is not actually allowed to "seize" your residence unless the tax bill you owe is $5,000 or more. There are no limitations as to the $50,000 exemption amount that you mentioned.