Been there done that.  Only mine was a 4X4 van.  Here are some good tips:

Bungee the stuff inside (handles vibrations well)

I bolted my roof top carrier to plywood attached to my roof rack.  No problems.  The roads are pretty good these days.

The Milepost is good.  So is a Topo map of the state (though you will see there aren't many roads).

Think about putting a basket on the roof for dirty smelly wet stuff (fish, muddy boots, waders, smoker, etc).

Take the Ferry at least one way from Prince Rupert to Haines.  You can jump on and off and really see the cool towns along the marine highway.  We never spent a night on a ferry, and the cost is the same no matter how many stops.

We took an Avon inflatable (12' with 10hp Mercury engine).  It was nice to have, but we did have a few leaks in glacier bay.

If you take the inside passage, GO TO GLACIER BAY.  Take the ferry to Juneau and another to Glacier bay.  We put our boat on the ferry and spent 12 days in the bay (went up 30 miles into the bay... AWESOME).

You WILL see bears.  Be ready.  Never carry food inside your pack and don't keep it in your camp.  Unless you really are Rambo, think twice about ever shooting one (if you do, make sure it is a high powered rifle.. forget handguns, can't take in Canada anyway)  Our policy was never shoot unless a bear touches one of us (we had Winchester Marine shotgun loaded with German rifled slugs).  We encountered many bears as close as 20 yds and never had a problem (other than the smell in our pants).  90+% of all charges are bluffs.  One shot and the bluff is called.  Wear bells, make noise, don't run.  BTW, dogs tend to go find bears, piss them off, then run back to you...

When you get there BUY the Alaska Tour Saver coupon book (one for each of you).  It will save you thou$ands.

If you will be there in Sept, put in for the drive pass in Denali.

Go to Denali often (June = spring, July = summer, Aug = winter).  It changes.

Bring lots of rain gear.  It WILL rain every day.  Be ready to deal with it and don't let it stop you.  Layers and goretex.  You will not have use for cotton clothing.

Get a good tent, boots, and pack.  Camping there is awesome.

Get used to the mosquitos.  Bring a head net if you must.

Buy a fishing license for the duration.  It will pay for itself with fresh trout and salmon (all you can bear to eat).  Bring fishing gear.  A light rod for trout, a 12lb test rod for salmon (you can go heavier, but I didn't).  We made our own salmon jerky with a cheap smoker from Kmart... yum yum.

You can free camp all the way up and back.  If you must, buy an Alaska State Campground pass for the summer.  Buy a National Parks Pass.

Get good tires.  I suggest BFG AT's even for your 2WD.  We rarely used 4X4, and the Dempster and Haul road will eat lesser tires.  Bring a spare and patch kit.  There is limited 4X4 opportunity as they really don't have many roads.

If you don't want to bring an inflatable, you can rent sea Kayaks in glacier bay, or maybe even a better place out of Whittier.

DO a flight seeing tour (coupons in toursaver). There is no better way to really SEE AK.

Do as many glacier and whale tours as you can (in the old days (2000) these were FREE in the toursaver book - we did 7-8 of them...)

Web access in libraries.

Cool places:

 Denali

 Talkeetna for the Moose Dropping Festival.  Maybe flight up to Denali base camp.

 The kenai

 Clam Gulch (in the Kenai)  Lots of long neck clams, don't forget the liguini.

 Wrangell St Ellias including Kennecott/McArthy (watch tires on this road).

 Homer (little sisters bakery, beautiful scenery)

 Seward (kings caught at the end of town by legal snagging) Le Barn Appetit for dinner.  Good aquarium.

 Exit Glacier (Seward).  Hike to top and spend the night in the cabin.

 Seward Harbor for Halibut (best kept secret).

 Talk to locals.  They are great and came up in a truck or van themselves before deciding to stay.