Looking for Engine Problems in 1999 Triton E-450 powering a Ford Motorhome

We have heard that the back spark plugs are problematic when it comes to replacing them. How accessible are those plugs? How much labour is involved in
replacing them. How does one get access to those back plugs? Is there a firewall hatch?
We are considering purchasing a 1999 Ford Motor Home that is powered by the 6.8 L Triton E450 gas engine. Before we buy we want to be certain that we are not buying a lot of expensive engine repairs in the future.
We want to hear the pros and the cons on this type of engine. So if you can provide such info, it would assist us in our decision to buy or not to buy. Thank You.
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