With 3rd-party sources available, one can reduce the tower shield's armor check penalty from −10 to at least −1...
- The armor and shield special ability maneuvering (Complete Book of Eldritch Might 163) (+1 bonus) and greater maneuvering (ibid.) (+2 bonus) reduce an armor or shield's armor check penalty by 2 and to 0, respectively. Yep, to zero. Straight up.
- Alternatively, for Pathfinder there's the celestial shield (Ultimate Equipment 131) (13,170; 7 lbs.), which weighs half the amount of a typical heavy steel shield but has no armor check penalty. After subtracting the cost for the masterwork heavy steel shield itself and the total +3 bonus, the celestial shield's remaining abilities ("It has no armor check penalty or arcane spell failure chance, and it allows the wielder to use feather fall on himself once per day") can be extrapolated to cost 4,000 gp. Talk to the DM.
But using exclusively Wizards of the Coast material to do this is, I think, impossible.
...But, sadly, nothing I've found permits making a shield bash with a tower shield
A tower shield (PH 123, 125) (30 gp; 45 lbs.) specifically can't be used to shield bash (PH 125). In fact, one can't even install on it shield spikes (PH 125). (True even in Third Edition, Plot and Poison being an unupdated Third Edition text.)
Green Ronin Publishing's Plot and Poison: A Guidebook to Drow, part of the publisher's Races of Renown line, lists as the entire benefit of the feat Shield Mastery as
Choose a type of shield (buckler, small, large, or tower). When you use that type of shield, its armor check penalty is reduced by 1. Armor check penalties cannot be reduced below 0. This feat may be chosen as a fighter bonus feat. (96)
Hence, one can't make a shield bash with a tower shield because of the feat Shield Mastery. Further, the benefit of the feat Shield Specialization is
When you make a shield bash attack with a type of shield selected for the Shield Mastery feat, you can regain the shield's armor bonus to your AC as a free action. If you choose the buckler for this feat, you can make shield bash attacks with it that deal 1d3 points of damage (×2 crit) and do not suffer the normal −1 penalty on off-hand attacks, whether with weapons or shield bashes. In addition, you can regain the buckler's AC bonus after making an attack with an off-hand weapon. This feat may be chosen as a fighter bonus feat. (96)
Thus, even if the tower shield is picked for use with the feat Shield Mastery, the feat Shield Specialization doesn't enable a tower shield to be used to make shield bashes. The text doesn't allow doing so in the same nonstandard way that is allowed with the buckler.
The benefit of the feat Double Shielding says in part that
You can make shield bash attacks with your primary hand, incurring no off-hand penalty, but you lose the armor bonus of that shield until your next action as normal. If you use two bucklers and employ two-handed weapons or ranged weapons that require two-hands (such as all bows and heavy crossbows) you incur a −2 penalty on all attack rolls. (91)
Most would read that benefit as Since one can't make a shield bash with a tower shield, the feat Double Shielding doesn't change that. Now, it's totally cool if the DM reads the benefit You can make a shield bash attack with your primary hand as also implying And the DM must concoct house rules for shield bashing with a tower shield, but that's not a reading I'd support. That's like taking a feat saying You can make an attack with a greatsword that does 6d10 damage or whatever and claiming that means a greatsword appears in the character's hand whenever he uses the feat and makes an attack.1
I spent some time searching through primary, secondary, and tertiary Dungeons and Dragons, 3rd Edition and 3.5 books, and making a shield bash with a tower shield seems impossible. Undoubtedly, there's some crazy publisher during the OGL boom that published a Tower Shield Bash feat or a slamming shield special ability or whatever, but I couldn't find a way to make a shield bash with a tower shield.
1 Okay, not really, but no analogy is perfect.