After going over and over this build, I think I may have discovered the best way to build him.
I think the key will be to utilize the new Kensai enhancements for fighters. This will allow me to get all the feats I need as well as boosting damage and crit range on the weapon, without depending on rage (so I can use UMD if I have to). 
Shooting for 18/2 at level 20.
Let me know what you think.
Code:
Character Plan by DDO Character Planner Version 2.96
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Level 16 Lawful Good Warforged Male
(14 Fighter \ 2 Rogue)
Hit Points: 300
Spell Points: 0
BAB: 15\15\20\25\25
Fortitude: 14
Reflex: 15
Will: 2
Starting Feat/Enhancement
Abilities Base Stats Modified Stats
(32 Point) (Level 1) (Level 16)
Strength 8 10
Dexterity 18 26
Constitution 16 20
Intelligence 12 12
Wisdom 6 6
Charisma 12 12
Tomes Used
+1 Tome of Strength used at level 1
+2 Tome of Dexterity used at level 1
+2 Tome of Constitution used at level 1
+3 Tome of Dexterity used at level 16
Starting Feat/Enhancement
Base Skills Modified Skills
Skills (Level 1) (Level 16)
Balance 6 11
Bluff 1 1
Concentration 4 5
Diplomacy 1 19
Disable Device n/a n/a
Haggle 1 1
Heal -2 -2
Hide 5 8
Intimidate 1 1
Jump 3 8
Listen -2 -2
Move Silently 5 8
Open Lock n/a n/a
Perform n/a n/a
Repair 1 1
Search 1 1
Spot -2 -2
Swim -1 0
Tumble 6 9
Use Magic Device 3 17.5
Level 1 (Fighter)
Feat: (Fighter Bonus) Dodge
Feat: (Selected) Exotic Weapon Proficiency: Great Crossbow
Level 2 (Fighter)
Feat: (Fighter Bonus) Mobility
Level 3 (Fighter)
Feat: (Selected) Rapid Reload
Level 4 (Fighter)
Feat: (Fighter Bonus) Point Blank Shot
Level 5 (Rogue)
Level 6 (Fighter)
Feat: (Selected) Shot on the Run
Level 7 (Fighter)
Feat: (Fighter Bonus) Rapid Shot
Level 8 (Fighter)
Level 9 (Fighter)
Feat: (Fighter Bonus) Improved Critical: Ranged Weapons
Feat: (Selected) Toughness
Level 10 (Rogue)
Level 11 (Fighter)
Level 12 (Fighter)
Feat: (Fighter Bonus) Precise Shot
Feat: (Selected) Weapon Focus: Ranged Weapons
Level 13 (Fighter)
Level 14 (Fighter)
Feat: (Fighter Bonus) Greater Weapon Focus: Ranged Weapons
Level 15 (Fighter)
Feat: (Selected) Weapon Specialization: Ranged Weapons
Level 16 (Fighter)
Feat: (Fighter Bonus) Greater Weapon Specialization: Ranged Weapons
Enhancement: Fighter Attack Boost I
Enhancement: Fighter Attack Boost II
Enhancement: Fighter Attack Boost III
Enhancement: Fighter Attack Boost IV
Enhancement: Fighter Haste Boost I
Enhancement: Fighter Haste Boost II
Enhancement: Rogue Skill Boost I
Enhancement: Fighter Critical Accuracy I
Enhancement: Fighter Critical Accuracy II
Enhancement: Fighter Critical Accuracy III
Enhancement: Fighter Critical Accuracy IV
Enhancement: Fighter Item Defense I
Enhancement: Rogue Sneak Attack Accuracy I
Enhancement: Rogue Sneak Attack Training I
Enhancement: Rogue Dexterity I
Enhancement: Fighter Strength I
Enhancement: Fighter Toughness I
Enhancement: Fighter Toughness II
Enhancement: Fighter Toughness III
Enhancement: Warforged Constitution I
Enhancement: Warforged Constitution II
Enhancement: Warforged Construct Thinking I
Enhancement: Warforged Construct Thinking II
Enhancement: Warforged Construct Thinking III
Enhancement: Warforged Healer's Friend I
Looking at final stats of:
16 Str
26 Dex (24 if I can't get a +3 tome)
20 Con
12 Int
12 Wis
18 Cha
Used (+6 stat items for dex, con, str, wis, and cha)
Hitpoints around
350-380 or so.
Final unbuffed saves (lvl 16) would be:
24 Fort (14 base +3 stat item +5 resist +2 kensai)
25 Reflex (15 base +3 stat item +5 resist +2 kensai)
15 Will (2 base +3 stat item +5 resist +2 kensai +3 Wf'd enhancements)
Lvl 16 Diplo would be:
19 base +3 stat item +6 shroud item +2 kensai +15 item = 45
Lvl 16 UMD would be:
17.5 +3 stat + 6 shroud +2 item, +2 boost = 30.50
Minimum Damage with non greensteel Great Xbow would be:
2D8 + 3 (bolts) + 1 (kensai 1) +1 (kensai II), + 2 fighter weapon focus, +2 fighter greater weapon focus
Crits would be:
2D8 +3, 3 (bolts) + 1 (kensai 1) +1 (kensai II), + 2 fighter weapon focus, +2 fighter greater weapon focus, +2 (kensai I), +2 (Kensai II) x2
Confirm crits would be boosted by +12!! (+8 fighter enhancements +4 Kensai)
The base to hit bonus would be something like:
+34 unbuffed. (15 bab, 11 dex, +3 bolts, +2 kensai I and II, +3 weapon focus)
+39 boosted (7 action boosts a day)
I think that is it. Don't know if I missed any damage in there??
Comments or criticisms welcome.
I think the loss of 1 on the crit range (from not going barb) would be more than made up for on the extra damage from Kensai and the weapon focus skills since those take effect on every hit?? Plus that effect is constant, not rage based so it wouldn't wear off and wouldn't affect UMD use.